1. Field of the Invention
The present invention relates to defect repairing in a graytone part in a graytone mask.
2. Description of the Related Art
In recent years, attempts have been made to reduce the number of mask sheets by using graytone masks in the field of large-sized LCD masks (as set forth in the monthly FPD Intelligence, May, 1999).
As shown in FIG. 8A, such a graytone mask has an opaque part 1, a transmission part 2 and a graytone part 3. The graytone part 3 corresponds to an area in which there is formed an opaque pattern 3a of below or equal to the resolution limit of an exposure apparatus for a large-sized LCD using the graytone mask and is designed to selectively change the thickness of a photoresist film by decreasing the light transmitted through this area so as to decrease the amount of irradiation due to the area. Normally, the opaque part 1 and the opaque pattern 3a are formed with films that are made of the same material such as chromium (Cr) or a chromium compound and have the same thickness.
The resolution limit of the exposure apparatus for the large-sized LCD using the graytone mask is about 3 xcexcm in the case of an exposure apparatus of a stepper type and about 4 xcexcm in the case of an exposure apparatus of a mirror projection type. Consequently, the space width of a transmission part 3b in the graytone part of FIG. 8A is set at less than 3 xcexcm and the line width of the opaque pattern 3a of below or equal to the resolution limit of the exposure apparatus is set at less than 3 xcexcm, for example. When the exposure apparatus for the large-sized LCD is used for light exposure, as the exposure light transmitted through the graytone part 3 as a whole is deficient in the amount of light exposure, positive photoresists are left on a substrate though the thickness of the positive photoresists exposed to light via the graytone part 3 solely decreases. More specifically, there arises a difference in solubility of resists in developing liquid between parts corresponding to the ordinary opaque part 1 and to the graytone part because of difference in the amount of light exposure and this results in, as shown in FIG. 8B, making a part 1xe2x80x2 corresponding to the ordinary opaque part 1 as thick as about 1.3 xcexcm, making a part 3xe2x80x2 corresponding to the graytone part 3 as thick as about 0.3 xcexcm and making a part corresponding to the transmission part 2 a part 2xe2x80x2 without resists, for example. A first etching of a substrate as a workpiece is carried out in the part 2xe2x80x2 without the resists so as to remove the resists in the thin part 3xe2x80x2 corresponding to the graytone part 3 by ashing and the like and by carrying out a second etching of this part, the etching process is performed with one mask instead of two masks as conventionally used in order to reduce the number of masks for use.
The above-mentioned repairing of defects in the graytone part in the graytone mask has been made in pursuit of restoring the same pattern as a regular pattern, that is, restoring the same form as the original one in the defective portion.
A specific conventional method of defect repairing will now be described.
FIG. 10A shows a condition such that the opaque pattern 3a in the graytone part 3 is formed with normal microscopic lines and spaces free from defects (line width=less than 3 xcexcm and space width=3 xcexcm).
FIG. 10B shows a condition such that part of the opaque pattern 3a in the graytone part 3 is missing.
FIG. 10C shows a conventional method of defect repairing. In case it is attempted to repair the defects by restoring the same line width as that of the normal opaque pattern 3a as in the prior art, since the line width of the normal opaque pattern 3a is as small as approximately 1 xcexcm. the formation of a repairing film 4 with the width that can be corrected (e.g., 2 xcexcm) by a laser CVD apparatus allows the line width in a repairing portion to grow as fat as 3 xcexcm, thus developing a problem in that a graytone effect equal to that in the regular pattern is unachievable. Moreover, the operation of aligning the position of the repairing film 4 has been troublesome and time-consuming as well. Although it appears to be easy to remove the fat portion of the line at a glance by a laser repair apparatus, there is the possibility of partially scraping the adjoining lines in case where the line alignment is shifted. The operation of not only performing the position alignment but also varying a slit form in conformity with a pattern form to be repaired by means of the laser repair apparatus has also been troublesome and time-consuming.
When it is attempted to restore the same form as that of the regular pattern in case where a opaque defect (e.g., a (short) bridge, a projection, a spot, etc.) is similarly repaired, the operation of not only performing the position alignment but also varying the slit in conformity with each defect size to be corrected by means of the laser CVD apparatus has been troublesome and time-consuming.
As the repairing of the graytone part is exhausting and time-consuming as stated above, it has practically been difficult to do such repairing.
An object of the invention is to provide a method of readily repairing defects in a graytone part which is practically difficult to repair by a conventional method of defect repairing.
The following arrangements are made according to the invention.
(Arrangement 1) A method of defect repairing in a graytone part in a graytone mask, which has a opaque part, a transmission part and the graytone part aimed at selectively varying the thickness of a photoresist film by decreasing the amount of light transmitted through an area wherein there is formed a opaque pattern of not exceeding the resolution limit of an exposure apparatus using the graytone mask, the method being characterized by forming such a repairing pattern as to make obtainable a graytone effect equal to the graytone effect of a regular pattern without restoring the same form as that of the regular pattern in the defective portion.
(Arrangement 2) A method of opaque defect repairing as described in Arrangement 1 is characterized by removing a film in a portion containing opaque defects to form a form and/or a disposition of achieving a graytone effect equal to the graytone effect of the regular pattern in order to form a repairing pattern different from the regular pattern.
(Arrangement 3) A method of clear defect repairing as described in Arrangement 1 is characterized by forming a repairing film to form a form and/or a disposition of achieving a graytone effect equal to the graytone effect of the regular pattern in order to form a repairing pattern different from the regular pattern.
(Arrangement 4) A method of clear defect repairing as described in Arrangement 1 is characterized by forming the repairing film in an area containing clear defects, then partially removing a repairing film to form a form and/or a disposition of achieving a graytone effect equal to the graytone effect of the regular pattern in order to form a repairing pattern different from the regular pattern.
(Arrangement 5) A method of defect repairing as described in Arrangement 2 is characterized by repairing by pre-fixing a slit form of a laser CVD apparatus for forming a repairing film or a slit form of a laser repair apparatus for removing the film to a slit form for use in achieving a graytone effect.
(Arrangement 6) A method of defect repairing in a graytone part in a graytone mask, which has a opaque part, a transmission part and the graytone part aimed at selectively varying the thickness of a photoresist film by decreasing the amount of light transmitted through an area wherein there is formed a opaque pattern of below or equal to the resolution limit of an exposure apparatus using the graytone mask, the method being characterized by forming a translucent film capable of controlling the amount of light transmitted through the film at least on a clear defective portion.
(Arrangement 7) A method of defect repairing as described in Arrangement 2 is characterized by repairing after removing at least a pattern which is located at periphery of the defect.
(Arrangement 8) A method of defect repairing as described in Arrangement 1 is characterized in that the graytone mask is a mask for an LCD.
According to Arrangement 1, by forming such a repairing pattern as to make obtainable a graytone effect equal to the graytone effect of a regular pattern, the graytone effect equal to the graytone effect of the regular pattern can be obtained without restoring the same form as that of the regular pattern in the defective portion. In such a repairing pattern as to make obtainable a graytone effect equal to the graytone effect of the regular pattern, the form of the repairing pattern is required not so much severely as compared with a case where the same form as that of the regular pattern is restored.
According to Arrangement 1, moreover, since the same form as that of the regular pattern is not restored, the trouble of restoring the same form as that of the regular pattern is saved, whereby it is possible to obviate a troublesome business arising from the operation of not only performing the position alignment but also varying the slit.
Thus, the repairing work can be done in a short time.
According to Arrangement 2, by removing a film in a portion containing opaque defects in the form and/or the disposition of achieving a graytone effect equal to the graytone effect of the regular pattern so as to form a repairing pattern different from the regular pattern, the operation of not only performing the position alignment but also varying the slit in conformity with each defect size to be corrected by means of a laser repair apparutus, that is, the troublesome and time-consuming operation that has heretofore been necessary for restoring the same form as that of the regular pattern by removing the whole opaque defective portion can be dispensed with.
According to Arrangement 3, by forming a repairing film in the form and/or the disposition of achieving a graytone effect equal to the graytone effect of the regular pattern so as to form a repairing pattern different from the regular pattern, the operation of not only performing the position alignment but also varying the slit of a laser CVD apparutus in conformity with each defect size to be corrected can be dispensed with, that is, the troublesome and time-consuming operation that has heretofore been necessary for restoring the same form as that of the regular pattern by filling up a clear defective portion.
According to Arrangement 4, by partially removing a repairing film in the form and/or the disposition of achieving a graytone effect equal to the graytone effect of the regular pattern after forming the repairing film in an area containing clear defects so as to form a repairing pattern different from the regular pattern, work and also working time can be made simpler and shorter than in Arrangement 3.
According to Arrangement 5, by pre-fixing the slit form, the operation of varying the slit can be dispensed with.
According to Arrangement 6, since a repairing film with the transmittance under control, any microscopic pattern of below or equal to the resolution limit of an exposure apparatus need not be formed.
According to Arrangement 7, it is unnecessary to make alignment of remaining portions of the opaque pattern that has undergone pattern-missing by removing the remaining portions thereof in the graytone part. Moreover, as a repairing pattern is uniformly formable over the whole defective area including an area with the pattern removed, a more uniform graytone effect is obtainable.
According to Arrangement 8, though there is no example wherein a translucent film is employed in a graytone mask for an ordinary semiconductor with the formation of a microscopic pattern of below or equal to the resolution limit of an exposure apparatus, assuming that there exists such a graytone mask as is formed with a microscopic pattern of below or equal to the resolution limit of an exposure apparatus, the graytone mask may be dealt with by the conventional method of defect repairing even when time and effort to a certain degree are needed as the mask size is small. In the case of a graytone mask for an LCD, however, the graytone mask therefor can hardly and actually be dealt with by the conventional method of defect repairing because it is large-sized and consequently has many defects. Therefore, the method of defect repairing according to the invention is indispensable for making a graytone mask for an LCD fit for practical use.
With the arrangements above, such a repairing pattern as makes obtainable a graytone effect equal to the graytone effect of the regular pattern has preferably xc2x115% of the transmittance of the regular pattern and more preferably xc2x110% thereof.